Modern appliances such as washing machines and dryers may provide for lid or door switches detecting when the appliance lid or door is open. In many cases, these lid switches serve to help protect the consumer from machinery moving inside the appliance by turning off an appliance motor or otherwise deactivating moving elements of the appliance. Such switches may include a stationary contact disconnecting from a movable contact driven by movement of a switch operator when the lid or door is open. The two contacts may control power to a motor or brake or the like.
Electrical switches normally provide a snap action mechanism so that the contacts of the switch open and close rapidly (to reduce arcing) independent of the speed of movement of the switch operator. One method of providing a snap action is a so-called “over-center spring” attached to a lever holding the movable contact. When the force applied on the lever by the over-center spring crosses the lever pivot (over-center), the torque on the lever rapidly switches direction causing the switch to “snap” between positions. The switch operator normally applies forces to the over-center spring rather than directly to the contact, so that the operator does not interfere with the snap action.
Voltage surges in the power line connected to an appliance can cause high currents through the contacts in switches of this type, welding the contacts together. In such cases, the force of the over-center spring on the welded contact may be insufficient to break the weld, with the result that the switch cannot be turned off. One solution is to increase the strength of the over-center spring, but this may be undesirable to the extent that it increases the operating force necessary to activate the switch, for example, preventing ready door closure. Increasing the strength of the over-center spring may also undesirably tax the other components of the switch.